From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49FF2CA9EC5 for ; Wed, 30 Oct 2019 16:19:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E3BD205C9 for ; Wed, 30 Oct 2019 16:19:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="G9hmuWiC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726900AbfJ3QTY (ORCPT ); Wed, 30 Oct 2019 12:19:24 -0400 Received: from mail-ua1-f67.google.com ([209.85.222.67]:42270 "EHLO mail-ua1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726261AbfJ3QTY (ORCPT ); Wed, 30 Oct 2019 12:19:24 -0400 Received: by mail-ua1-f67.google.com with SMTP id v2so873592uam.9; Wed, 30 Oct 2019 09:19:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=lnGL5M5fSCWAymH5l1Oh8Q43QFPNjJp2zZ+3UI6AZG0=; b=G9hmuWiCf5if5Wz6RgyTUBMpAyMnrHgc+JT1dhYZAP2ulDhUvChvkINVBjMFv3fpK6 7KOEV8FGzHMxNSCGEtzq0IWmNIwh1lZaDYj7vQ5UQRS7KePLCkeU1S40QJrVPxJ1JNbq D8n9GGHWTUarE1/jkqC4oh0qitszppCyrKyXBeWdAlW8lx1XZAvl+EYftidrzaIj7Len 9GHRSPEK0NVvxivPEj+ykfPaTmwgPitpsqwjhgbIVZdkkJQ8Mym45GGZSvw8qakDAyyn dkxYPspM4ip86vauXWiNyHiHVFdlnfk4Vw6pyolJUslaflLju4D8FtfjJWZlW0EeBqmo m4Kg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=lnGL5M5fSCWAymH5l1Oh8Q43QFPNjJp2zZ+3UI6AZG0=; b=KN7cyg1YeygLPMip5QL+arkV0knn03bnXECCM/IDJc03CpLSjvd9Vvc0WxvW6pNQSx sYFIkIGSjuumCskF3XpS0GPVZEUT4tAeMJROaPh8nSJpM0mFWD/VLq086FZ4UjNSeodK SE1F1qnfnD4FBaloH7tcia35MDqGWO9aLktxiC0HYF+1/2It+GYJtUCWIeFimsKYmCTn sT0rV4pRwxpy/q7bW29r6IcC5//n/Zq3KtOntxKnjVkGd4PH8PTmz0+5tVW+ox2FPOhf gzYtNCVNuQlp9QuHWNGhaMYDSeNT+C1p6ren1k7yv2DEYBA41eVE1zvUMzFgo8fgpE8V sglw== X-Gm-Message-State: APjAAAU3WDi3Ztvt6qp5ZMefBAt6A4nhE0isP4kpxMdeGpKB9+91yqoT wPnz1UvIb7vxMricdmdMXYA5bL392mFoeQoNEoU= X-Google-Smtp-Source: APXvYqxSzS7R7XJBRTYj3i0gKkKDByOF9kfUI8Mz9RHF/Ln+fYDL+Jh0W+wMHUiALORqI5T3zgyZOja4yoeK1DYlRAo= X-Received: by 2002:ab0:2e9c:: with SMTP id f28mr298704uaa.20.1572452363034; Wed, 30 Oct 2019 09:19:23 -0700 (PDT) MIME-Version: 1.0 References: <20191028141053.12267-1-ethercflow@gmail.com> In-Reply-To: From: Wenbo Zhang Date: Thu, 31 Oct 2019 00:19:15 +0800 Message-ID: Subject: Re: [PATCH bpf-next v4] bpf: add new helper fd2path for mapping a file descriptor to a pathname To: Andrii Nakryiko Cc: bpf , Yonghong Song , Daniel Borkmann , Networking Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org > from what I can see, we don't have any BPF helper with this naming > approach(2 -> to, 4 -> for, etc). How about something like > bpf_get_file_path? I think bpf_get_file_path is better. I'll change to it. > > + * Description > > + * Get **file** atrribute from the current task by *fd*, t= hen call > > + * **d_path** to get it's absolute path and copy it as str= ing into > > + * *path* of *size*. The **path** also support pseudo file= systems > > + * (whether or not it can be mounted). The *size* must be = strictly > > + * positive. On success, the helper makes sure that the *p= ath* is > > + * NUL-terminated. On failure, it is filled with zeroes. > > + * Return > > + * 0 on success, or a negative error in case of failure. > Mention that we actually return a positive number on success, which is > a size of the string + 1 for NUL byte (the +1 is not true right now, > but I think should be). I agree. > I haven't followed previous discussions, so sorry if this was asked > before. Can either fdget_raw or d_path sleep? Also, d_path seems to be > relying on current, which in the interrupt context might not be what > you really want. Have you considered these problems? Yes, I've checked fdget_raw, it use atomic and rcu_read_lock/ruc_read_unloc= k, so it's not sleepable. d_path use rcu_read_lock/rcu_read_unlock too. In my mind I think this helper won't be called in the interrupt context (Would you please give me an example if there's an application scene). So I think it's ok to use d_path here. > > + if (!f.file) > > + goto error; > > + > > + p =3D d_path(&f.file->f_path, dst, size); > > + if (IS_ERR_OR_NULL(p)) { > > + ret =3D PTR_ERR(p); if p can really be NULL, you'd get ret =3D=3D 0 here, which is probably not what you want. But reading d_path, it seems like it's either valid pointer or error, so just use IS_ERR above? Agree, I'll fix error handling code. > > + goto error; > > + } > > + > > + ret =3D strlen(p); > > + memmove(dst, p, ret); > > + dst[ret] =3D '\0'; I think returning number of useful bytes (including terminating NUL) is good and follows bpf_probe_read_str() convention. So ret++ here? Agree. Thank you. > + goto end; > + > +error: > + memset(dst, '0', size); > +end: > + fdput(f); > + return ret; > +} > + [...] Andrii Nakryiko =E4=BA=8E2019=E5=B9=B410=E6=9C= =8830=E6=97=A5=E5=91=A8=E4=B8=89 =E4=B8=8A=E5=8D=882:48=E5=86=99=E9=81=93= =EF=BC=9A > > On Mon, Oct 28, 2019 at 1:59 PM Wenbo Zhang wrote: > > > > When people want to identify which file system files are being opened, > > read, and written to, they can use this helper with file descriptor as > > input to achieve this goal. Other pseudo filesystems are also supported= . > > > > This requirement is mainly discussed here: > > > > https://github.com/iovisor/bcc/issues/237 > > > > v3->v4: > > - fix missing fdput() > > - move fd2path from kernel/bpf/trace.c to kernel/trace/bpf_trace.c > > - move fd2path's test code to another patch > > > > v2->v3: > > - remove unnecessary LOCKDOWN_BPF_READ > > - refactor error handling section for enhanced readability > > - provide a test case in tools/testing/selftests/bpf > > > > v1->v2: > > - fix backward compatibility > > - add this helper description > > - fix signed-off name > > > > Signed-off-by: Wenbo Zhang > > --- > > include/uapi/linux/bpf.h | 14 +++++++++++- > > kernel/trace/bpf_trace.c | 40 ++++++++++++++++++++++++++++++++++ > > tools/include/uapi/linux/bpf.h | 14 +++++++++++- > > 3 files changed, 66 insertions(+), 2 deletions(-) > > > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > index 4af8b0819a32..124632b2a697 100644 > > --- a/include/uapi/linux/bpf.h > > +++ b/include/uapi/linux/bpf.h > > @@ -2775,6 +2775,17 @@ union bpf_attr { > > * restricted to raw_tracepoint bpf programs. > > * Return > > * 0 on success, or a negative error in case of failure. > > + * > > + * int bpf_fd2path(char *path, u32 size, int fd) > > from what I can see, we don't have any BPF helper with this naming > approach(2 -> to, 4 -> for, etc). How about something like > bpf_get_file_path? > > > + * Description > > + * Get **file** atrribute from the current task by *fd*, t= hen call > > + * **d_path** to get it's absolute path and copy it as str= ing into > > + * *path* of *size*. The **path** also support pseudo file= systems > > + * (whether or not it can be mounted). The *size* must be = strictly > > + * positive. On success, the helper makes sure that the *p= ath* is > > + * NUL-terminated. On failure, it is filled with zeroes. > > + * Return > > + * 0 on success, or a negative error in case of failure. > > Mention that we actually return a positive number on success, which is > a size of the string + 1 for NUL byte (the +1 is not true right now, > but I think should be). > > > */ > > #define __BPF_FUNC_MAPPER(FN) \ > > FN(unspec), \ > > @@ -2888,7 +2899,8 @@ union bpf_attr { > > FN(sk_storage_delete), \ > > FN(send_signal), \ > > FN(tcp_gen_syncookie), \ > > - FN(skb_output), > > + FN(skb_output), \ > > + FN(fd2path), > > > > /* integer value in 'imm' field of BPF_CALL instruction selects which = helper > > * function eBPF program intends to call > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > index 571c25d60710..dd7b070df3d6 100644 > > --- a/kernel/trace/bpf_trace.c > > +++ b/kernel/trace/bpf_trace.c > > @@ -683,6 +683,44 @@ static const struct bpf_func_proto bpf_send_signal= _proto =3D { > > .arg1_type =3D ARG_ANYTHING, > > }; > > > > +BPF_CALL_3(bpf_fd2path, char *, dst, u32, size, int, fd) > > +{ > > + struct fd f; > > + char *p; > > + int ret =3D -EINVAL; > > + > > + /* Use fdget_raw instead of fdget to support O_PATH */ > > + f =3D fdget_raw(fd); > > I haven't followed previous discussions, so sorry if this was asked > before. Can either fdget_raw or d_path sleep? Also, d_path seems to be > relying on current, which in the interrupt context might not be what > you really want. Have you considered these problems? > > > + if (!f.file) > > + goto error; > > + > > + p =3D d_path(&f.file->f_path, dst, size); > > + if (IS_ERR_OR_NULL(p)) { > > + ret =3D PTR_ERR(p); > > if p can really be NULL, you'd get ret =3D=3D 0 here, which is probably > not what you want. > But reading d_path, it seems like it's either valid pointer or error, > so just use IS_ERR above? > > > + goto error; > > + } > > + > > + ret =3D strlen(p); > > + memmove(dst, p, ret); > > + dst[ret] =3D '\0'; > > I think returning number of useful bytes (including terminating NUL) > is good and follows bpf_probe_read_str() convention. So ret++ here? > > > + goto end; > > + > > +error: > > + memset(dst, '0', size); > > +end: > > + fdput(f); > > + return ret; > > +} > > + > > [...]